The present invention is directed to a lung water computer system. In particular, the invention is directed to a software controlled data acquisition scheme for rapidly detecting concentrations of ICG and DHO tracers in a patient's blood over a relatively short interval of time such as 30 seconds. The invention may also be employed to detect constituents of food stuffs, gases, etc. The number of data samples may be varied adaptively over a wide range of sample levels or signal to noise (S/N) ratios.
The invention utilizes a single optical detection path and a single beam of VIS and IR radiation. The concentrations of DHO and ICG in the patient's blood are monitored over time and stored in memory to enable a software calculation of lung water.
Other systems for computing lung water using ICG and DHO tracers are known. Such systems, however, do not permit software control of data acquisition or adaptive control of the number of data samples. Such a system is disclosed in Basset et al, "Simultaneous Detection Of Deuterium Oxide And Indocyanine Green In Flowing Blood", Journal of Applied Physiology, pp. 1367-1371 (1981). In the Basset et al system, two separate beams are employed, one sample beam and one reference beam. The beams are identical. One beam is passed through a silica sample cell, and the other beam is passed through a reference cell which is an absorber of variable optical density. A mechano-optical device splits the beam passed by the cells into four beams, two sample beams and two reference beams. One sample beam and one reference beam are fed to a filter centered at an absorption peak of one tracer, and the other sample and reference beam are fed to an interference filter centered at the absorption wave length of the other tracer. The output of each filter is fed to an associated detector. One detector is a ICG detector, and the other detector is a DHO detector. The DHO detector may be a pyroelectric detector, and the ICG detector may be a silicon (Si) photodiode. The detector outputs are amplified by synchronous amplifiers and the amplified signals are plotted using a potentiometric recorder. The sampled recorded data is fed to a Commodore PET 2001 microcomputer to calculate flow rate, mean transit time, and lung water. The computer does not control the mode of data acquisition.
The system described in Basset et al suffers from certain disadvantages. Since two separate beams are employed, the system requires associated mechano-optics to split the beams into two separate optical channels. In addition, two separate detectors are required. Moreover, the silica sample cell is known to have a cut-off objectionably close to the DHO absorption peak (approximately 4.0 microns). Further, data acquisition is not computer controlled nor is it adaptive, that is, the number of samples is not variable as a function of sample level or S/N. In addition, the pyroelectric detector chosen for the Bassett et al system is slow responding (1-4 hz) in comparison to PbSe which can respond to a chopping rate up to 200 Khz.
The present invention also has application in the detection of other tracers or constituents of a fluid sample, in the detection of constituents of gases such as anesthetic gases, in the detection of minerals in an air-borne ground scanning system, and in the detection of color and content of foodstuffs.